1. Field
The present application relates to a method and apparatus for improving a 3D+time reconstruction based on X-ray angiography using non-invasive 3D imaging modalities.
2. State of the Art
Angiography is a commonly used imaging modality within a numerous variety of interventions. During such interventions it is very important that the clinician gets a good understanding of the object in question. For example, in vascular interventions it is important that the clinician has all information concerning the part of the vessel tree of interest. This is necessary when, for instance, a stent is to be placed in a bifurcated vessel, where a bifurcated vessel is a main artery or vein that has split up into two or more further arteries or veins.
Two dimensional angiographic imaging, such as X-ray, frequently lacks the possibility to visualize the bifurcation region correctly. Especially the carina position of the bifurcation, which is defined as the point where the vessel splits, is a challenge to visualize correctly with two dimensional angiographic imaging because of overlap of one or more of the vessel segments connected to the bifurcation.
If the physician bases his or her decision on incomplete or imprecise information about this bifurcated tubular shaped object, this can have severe consequences. For instance, an obstruction at the bifurcation can be missed or underestimated or the wrong stent dimension can be selected. This can lead to serious complications for the patient.
In practice interventional treatment is generally performed under guidance of 2D images acquired with angiographic X-ray systems of the so-called C-arm or L-arm type. These systems allow acquisition of 2D images from different directions, also called 2D perspectives, of the object under examination. These different perspectives can be obtained by rotating the arm holding the X-ray source and the image intensifier around the patient.
Making a 3D reconstruction from 2D images acquired in at least two different perspectives is done frequently, however there remains some uncertainty also in the 3D reconstruction on the exact shape of the vessel around the bifurcation due to overlap in the 2D images used to make a 3D reconstruction of the bifurcated vessel.
An example of the problems with overlap is visualized in FIG. 1. Only the last image shows the true shape of the bifurcation resulting in a proper visualization of the carina.
For the 3D reconstruction it is therefore important that the 2D angiographic images are taken from a right perspective. In the case of angiographic systems, the right perspective is defined as the angulations of an X-ray system (both the system rotation and angulation) that contains as much information as possible. In this perspective foreshortening and overlap of surrounding vessels should be minimized.
Foreshortening is the event when an object seems compressed when viewed from a certain perspective, causing distortion in the information.
When dealing with complex vessels such as the left coronary artery, overlap with other vessels can occur as seen in FIG. 2. Because these branches can be of the same coronary artery and for instance bifurcate after the admission point of the contrast, the appearance can be drawn that a section of interest contains contrast. This can lead to a missed or underestimated obstruction in the section of interest.
To be able to cope with this misinterpretation, the clinician needs to have a good understanding of the entire coronary tree. However, with X-ray angiography it is not possible to reconstruct the entire coronary artery tree using two 2D angiographic images. This is due to the field of view (FOV) of the X-ray modality as seen in FIG. 3 and the contrast wash out.
Also when dealing with for instance coronary arteries, multiple bifurcations can exist in a segment of interest. These bifurcations each have a different orientation. Therefore, it is almost impossible to visualize every bifurcation region correctly using X-ray.
A further aspect that needs to be taken into account is the movement of the coronary tree during a heart cycle. This movement can for instance be caused by the motion of the heart itself but also by the breathing of the patient. During these movements, different sections of the coronary tree move relative to each other. This movement can cause overlap of vessels in the chosen 2D perspectives in certain stages of the heart cycle and makes understanding the coronary tree at a given time an even more complex task.
In current practice movement of the vessels of interest during angiography is determined during continuous contrast admission throughout multiple heart cycles, which allows the clinician to follow the movement of the coronary arteries in X-ray angiographic images. This is a large burden for the patient. Of these continuous recordings multiple 3D reconstructions can be made. However, to obtain the optimal amount of information for these 3D reconstructions, each reconstruction needs to be made using optimal projections. In practice this is however not feasible. Therefore, most of these reconstructions are made using one or more perspectives that is optimal for one moment in time. This can cause discontinuities between the 3D reconstructions.
An alternative for making various separate 3D reconstructions is the propagation of the 3D reconstruction in the time domain (4D) as taught by Chen et al, “Kinematic and Deformation Analysis of 4-D Coronary Arterial Trees Reconstructed From Cine Angiograms”, IEEE Transactions on medical imaging, Vol. 22, No. 6, June 2003 pp 710-721 and Zheng et al, “Sequential reconstruction of vessel skeletons from X-ray coronary angiographic sequences”, Computerized Medical Imaging and Graphics 34 (2010) 333-345. However, the information that can be gathered using this approach is limited due to the aforementioned limitations of X-ray such as FOV, overlap and the presence of multiple bifurcations. A way to acquire information regarding multiple bifurcations without undistinguishable overlap is through volumetric images acquired with CT or MR systems.
However, these imaging acquisition systems cannot be used during interventions. Also CT recordings are single phase recordings, including only one heart phase per recording. Furthermore, the spatial resolution and/or temporal resolution of CT and MR imaging modalities is significantly lower than of X-ray angiography.
Therefore, the 3D imaging modalities by themselves are not applicable nor sufficient to obtain all information needed during the intervention, they do however contain important information regarding bifurcations, overlap and diseased segments.
Furthermore, data obtained earlier on from a 3D imaging modalities can be used to guide a clinician during an intervention for instance for vessel matching.
Baka, at al presented a method for guidance during coronary intervention on a monoplane x-ray system, “Respiratory motion estimation in x-ray angiography for improved guidance during coronary interventions”, Physics in Medicine & Biology, 60 (2015) 316-3637. The described method is based on retrieving of the 3D coronary artery centerline from pre-interventional 3D CT images. To achieve the improved guidance, a framework is presented for registration of the 3D centerlines with the monoplane X-ray image sequences in which the patient specific cardiac and respiratory motion is learned. Although the method uses 3D coronary centerline reconstructions obtained by pre-interventional 3D CT imaging and monoplane X-ray angiography to learn the motion within this specific X-ray angiographic image perspective, the method is restricted to guidance within this specific X-ray angiographic image perspective. During coronary interventions is common practice that the physician uses multiple perspectives of the X-ray system (angulating, rotating the X-ray system) to obtain a desired perspective of the object of interest, which significantly limits the clinical application of this solution.